1. Field of the Invention
The present invention relates to an encoder that detects a position of an object.
2. Description of the Related Art
Previously, there is an optical apparatus such as a lens apparatus or a camera that has an autofocus (AF) function. The AF function is achieved by a focus detection system that detects an in-focus state of an object, a lens drive system that moves a focus lens so as to form an object image on an image pickup element, and an AF control system that controls the focus detection system and the lens drive system. The focus detection system performs focus detection by a phase difference method, a contrast method, or the like. The lens drive system is provided with an encoder that detects a position of the focus lens. The AF control system controls a motion of the focus lens based on an output of the encoder.
Japanese Patent Laid-Open Nos. 2011-99869 and 2007-47652 disclose an optical encoder including a reflection scale. This reflection scale is adhesively fixed on an inner surface of a scale supporting body (or, a roller ring) by using a double-faced tape.
Recently, the demand of a higher-accuracy AF is increasing in order to obtain an image which is focused on an object with higher accuracy, and therefore an encoder capable of performing position detection with higher accuracy and higher resolution is required. However, in each of the configurations of Japanese Patent Laid-Open Nos. 2011-99869 and 2007-47652, it is difficult to perform the position detection with high accuracy and high resolution. In other words, the accuracy to be ensured by the reflective pattern is limited since there is a variation of a partial thickness of the double-faced tape, a strain of the scale that is generated when attaching the scale, a strain that is generated by the expansion and contraction of the scale in accordance with a temperature change or a humidity change, or the like.